Service rigs are used in a wide range of oil field services, including but not limited to, logging, cleanouts, fracturing, cementing, underreaming, fishing, completion and production. Such services often require several lengths of steel pipe to be made up (i.e., successive lengths of pipe are connected together in an end-to-end fashion) as they are extended into the well bore, and subsequently broken down (i.e., successive lengths of pipe are disconnected) as they are withdrawn from the wellbore.
To facilitate service rig operations, mobile service rigs have been developed that can be mounted to a wheeled transport carrier, and driven to the relevant well site. The rigs comprise certain conventional elements, namely: a wheeled platform or frame forming the base of the rig; a mast to elevate the blocks; an elevator above the wellhead; a control center for the operator; and a power source for system power.
However, these existing service rigs have certain limitations. One limitation of existing mobile service rigs is their inability to store and handle pipe at the well site. Accordingly, a separate pipe rack and catwalk must be provided at the well site. Further, a second transport carrier is needed to move the pipe rack and catwalk to the well site, and to position them inline with the service rig. This can be challenging in congested well site environments. It also requires time during which the service rig cannot be used.
A further limitation of existing mobile service rigs is that their masts have limited length. Transportation laws regulate the maximum permissible length of overhangs at each end of the transport carriers. Further, the weight of the mast needs to be balanced over the axles of the transport carrier to maintain safe handling characteristics of the transport carrier. At the same time, however, the masts are attached to the frames at a fixed position so that, when the masts are erected, their mast bases will engage the ground surface. These competing considerations prevent the masts from reaching their potential lengths.
Still a further limitation of existing service rigs is that their draw works are driven indirectly by an engine through a gearbox and drive line. As the engines accelerate to their power band, the amount of power supplied to the draw works varies. This can make it difficult to precisely control the draw works. When the engines are operating out of their power band, their fuel efficiency is sub-optimal. Further, the gearbox and drive line result in mechanical losses of the engine's power, thus decreasing the overall efficiency of the draw works.
Accordingly, there is a need for a mobile service rig that mitigates at least some of the limitations of mobile service rigs in the prior art.